Nanofibers are used in a variety of applications such as filters for water purification, filters for air purification, composites, membranes for cells and the like, in particular, reinforced composite membranes for fuel cells for cars, due to wide surface area and excellent porosity.
A fuel cell is an electrochemical device which is operated from hydrogen and oxygen as fuels, which arises as an environmentally friendly device because its products are pure water and recyclable heat. In addition, it is widely used as power sources for household, car and power generation applications and the like owing to advantages such as easy operation, high output density and non-noise.
Depending on the type of electrolyte membrane, the fuel cell is classified into an alkaline electrolyte fuel cell, a direct oxidation fuel cell, a polymer electrolyte membrane fuel cell (PEMFC) and the like. Of these, the polymer electrolyte membrane fuel cell generates electricity based on transfer of hydrogen ions (H+) from an oxidation electrode (anode) to a reduction electrode (cathode), which can operate at room temperature and have an advantage of short activation time, as compared to other fuel cells.
A polymer electrolyte membrane fuel cell includes an electricity generator which includes a membrane electrode assembly (MEA) which is provided with an oxidation electrode and a reduction electrode which are opposite to each other based on a polymer electrolyte membrane fuel cell interposed therebetween, and a separator (also, referred to as a “bipolar plate”), a fuel supply to supply a fuel to the electricity generator, and an oxidizing agent supply to supply an oxidizing agent such as oxygen or air to the electricity generator.
A polymer electrolyte membrane is a conductor of hydrogen ions and may be classified into a single membrane including a polymer such as a fluorine- or hydrocarbon-based polymer and a composite membrane including a composite of the polymer with an organic/inorganic substance, a porous support or the like. The most generally used single membrane is Nafion™ available from DuPont which is a perfluorine-based polymer. However, Nafion™ has drawbacks of high price, low mechanical shape stability, and high membrane resistance due to high thickness.
In order to solve these drawbacks, a research is underway on composite membranes with reinforced mechanical shape stability. Of composite membranes, a pore-filling membrane including a porous support impregnated with an ion conductor is actively researched due to low price as well as excellent performance and mechanical shape stability.
The support generally used for pore-filling membranes is polytetrafluoroethylene (PTFE). However, a PTFE support has superior chemical resistance, but has a drawback of low porosity of 40 to 60%.